This invention relates to controllers for electrically actuated braking systems such as those used to apply the brakes of towed vehicles, i.e., trailers, in response to commands from the towing vehicle. More particularly, the invention relates to electronic controllers for braking systems which operate in response to inertial sensors and/or manually actuated switches, or the like, to actuate a towed vehicle's brakes in a particular controlled manner.
Substantial effort and progress has been made towards the goal of providing more stable and more responsive electronic brake system controllers which actuate the electromagnetic brake shoe actuators of a towed vehicle. For example, it is known that continuous braking excitation is likely to promote trailer brake lockup which causes a substantial decrease in braking efficiency and loss of operator control. Prior art brake controllers have eliminated these undesirable effects by applying pulsating excitation to the brakes by means of a constant pulse width applied at varying frequencies or a varying pulse width applied at a constant frequency. It is also known that trailer brake lockup may occur if the towed vehicle's brakes are applied too rapidly. However, the brakes may feel sluggish and may not be fully actuated in a timely manner if the brake current is applied too slowly. Prior art controllers have been designed to apply current to the brakes in a controlled manner which avoids these problems and which releases the brakes rapidly when the brake actuation signal is removed to prevent continued actuation of the towed vehicle's brakes. Another example of progress in prior art brake controllers is the accommodation of different towed vehicle weights and brake system characteristics which are variables having a substantial impact upon the proper braking of the towed vehicle.
Although substantial progress has been made in brake system controllers, most of these prior art devices have relied on the extensive use of analog technologies to implement the controller circuitry. There are several drawbacks to these analog designs. First, analog circuits often exhibit operational variations (drift) over temperature extremes and component variability. Second, because the operation of the controller is hardwired into the design of the circuitry, these prior art devices have only limited flexibility which necessitate complete redesigns of the circuitry when changes are desired in the brake controller operational parameters or when the addition of new operational features are desired. Finally, since analog, designs rely on small variations in voltage during normal operation, they are often sensitive to voltage fluctuations and radio frequency noise sources which may cause operational problems.